RF amplifier with linear gain control
First Claim
1. A circuit for amplifying an input radio frequency (RF) band of signals, wherein signal gain in decibels (dB) is a linear function of the logarithm of a control signal, said circuit comprising:
- a first transistor amplifier stage having an output node exhibiting a first RF complex admittance within said frequency band of signals;
a second transistor amplifier stage having a control electrode, a second electrode coupled to a power supply and a third electrode coupled through a resistance to a common potential, said control electrode coupled to said output node and exhibiting a second RF complex admittance within said frequency band of signals;
PIN diode means connected between a control signal input and said output node and responsive to a control signal to reflect a given RF admittance, said PIN diode means further connected via an RF path to said common potential; and
RF reactance means shunt connected with respect to said PIN diode means, between said common potential and said output node, said RF reactance means having a third RF complex admittance that is chosen to negate imaginary portions of said first and second complex admittances, whereby any admittance seen by said PIN diode means is substantially real within said frequency band of signals.
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Accused Products
Abstract
A circuit amplifies an input RF band of signals and exhibits a signal gain in decibels that is a linear function of the logarithm of a control signal input. The circuit comprises a first amplifier stage having an output node that exhibits a first RF complex admittance within the RF band of signals. A second amplifier stage has an input node coupled to the output node of the first amplifier stage and exhibits a second RF complex admittance within the RF band of signals. A PIN diode, used as a gain control element, is shunt connected between the control signal input and the output node. An RF reactance circuit is also shunt connected between the output node and a common potential. The RF reactance circuit has a third admittance that is chosen to negate the imaginary portions of the first and second complex admittances, whereby the total admittance is substantially real and enables the PIN diode to see a minimal resistive load.
8 Citations
8 Claims
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1. A circuit for amplifying an input radio frequency (RF) band of signals, wherein signal gain in decibels (dB) is a linear function of the logarithm of a control signal, said circuit comprising:
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a first transistor amplifier stage having an output node exhibiting a first RF complex admittance within said frequency band of signals; a second transistor amplifier stage having a control electrode, a second electrode coupled to a power supply and a third electrode coupled through a resistance to a common potential, said control electrode coupled to said output node and exhibiting a second RF complex admittance within said frequency band of signals; PIN diode means connected between a control signal input and said output node and responsive to a control signal to reflect a given RF admittance, said PIN diode means further connected via an RF path to said common potential; and RF reactance means shunt connected with respect to said PIN diode means, between said common potential and said output node, said RF reactance means having a third RF complex admittance that is chosen to negate imaginary portions of said first and second complex admittances, whereby any admittance seen by said PIN diode means is substantially real within said frequency band of signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification